Varieties affect rice blast damage

Arkansas rice producers have seen bumper yields over the last few years, despite planting vast rice acreage in blast-susceptible varieties (some estimates put the number well above 55 percent). Among researchers, this is both a blessing and matter of concern.

Wells, a blast-susceptible variety, is planted on at least 45 percent of the state's acreage. “On the susceptibility scale (with 0 being resistant and 9 being extremely vulnerable), Wells is 6.5,” says Fleet Lee, a rice disease expert at the Rice Research Station and Extension Center in Stuttgart, Ark. “Cypress has the same rating. Francis and LaGrue are even higher — around 7.5.”

Wells is gaining in popularity. With a high-yield potential, growers gravitate towards it. But it isn't for every situation.

“Forcing a susceptible variety into an environment it isn't suited for is a bad idea,” says Lee. “I'm seeing more of that, and it worries me.”

This season blast has hit the state's rice worse than expected.

“We thought with the weather patterns we had, it wouldn't be as bad,” says Rick Cartwright, Extension plant pathologist. “But it's tearing up some of our fields. We've estimated yield losses at 10 percent up to 50 percent. The problem fields aren't centralized, they're scattered throughout the state.”

There is a common factor: the blast is usually seen in fields planted to the wrong variety. “Putting a blast-susceptible variety on light soils is a bad idea from the outset,” says Cartwright. “It's even worse if the grower can't manage water on the field well. Don't plant a variety like Francis — high-yielding but susceptible to blast — in light soils. In that situation, a field can be absolutely hammered, two fungicide applications or not.”

Even in cases where farmers have followed expensive fungicide recommendations “to a T,” says Cartwright, fields are badly damaged. The rule of thumb: if your field can't hold water, don't plant blast-susceptible varieties.

In most cases, says Lee, blast resistance can be naturally flood-induced. “If you put a flood on and hold it, a rice plant (through natural processes involving ethylene hormone production in root tissue) will become resistant to blast. The flood's depth and duration are very important. That's why it's unwise to plant susceptible varieties on soils that percolate easily.”

The flood inducement has been known for many years. However, the mechanics of it are just becoming understood.

“We've been looking at induced resistance since the mid-1980s, when blast in Newbonnet ate our lunch,” says Lee. “Back then, several astute growers noticed that where soils didn't percolate water rapidly, the blast wasn't so bad. We latched onto that and have studied it since.

“Our findings on ethylene are exciting, but they only carry us so far: high-yielding varieties are attractive, but their disease limitations can be too much to overcome.”

Growers should consider several factors in variety selection. Chiefly, don't think in terms of planting one variety across an entire farm. Match varieties to specific fields. What will perform best?

“We harp on this every year but still run into bad planting decisions all the time,” says Cartwright. “We spent the last two years saying, ‘Don't put Francis on sandy fields.’ Even so, we still have some, and those fields have major yield losses.”

Further, new rice varieties are appearing regularly. “It's almost like having all the options of other row crops now,” says Cartwright. “Growers should take advantage of that.”

In a sandy field, a 160-bushel yield from a resistant variety looks good compared to a variety with a 200-bushel potential that only produces 100.

“You can make 60 bushels by picking the right variety,” says Cartwright. “Don't consider it as losing 40 bushels, think of it as gaining 60. Some Clearfield 161 producers already think like that. The variety doesn't have the highest potential, except in a red rice field. If you've got heavy red rice, 160 bushels from Clearfield will be the clear winner.”